CN103993140A - A spheroidizing annealing process for low-hardness fastener wire - Google Patents

Abstract

The invention discloses a spheroidizing annealing process of a low-hardness fastener wire rod, which comprises the following steps: placing the fastener wire in a heat treatment furnace, filling protective gas into the heat treatment furnace, raising the temperature in the furnace to 710-730 ℃, and preserving the heat for 2-4 h; cooling in the first stage: cooling the temperature in the furnace to 660-680 ℃ at the speed of 20 ℃/h, and preserving the temperature for 2-4 h; cooling in the second stage: continuously cooling the temperature in the furnace to 600-620 ℃ at the speed of 10 ℃/hour; and cooling in the third stage: and naturally cooling the fastener wire to the normal temperature. The fastener wire processed by the process method has uniform metallographic structure, fine grains, low hardness, high toughness and high ductility, meets the requirements of fastener products which are high in difficulty and formed by multiple times of plastic processing, and has low product forming cracking rate.

Description

A spheroidizing annealing process for low-hardness fastener wire

Technical field:

The invention relates to an annealing process for metal materials, in particular to a spheroidizing annealing process for low-hardness fastener wires.

Background technique:

Spheroidizing annealing is one of the basic ways to improve the structure and properties of steel. The main purpose of spheroidizing annealing is to spheroidize carbides in the microstructure of steel materials, reduce the hardness of materials, improve the plasticity of materials, and reduce the deformation resistance of materials. , making the material easy to plastic processing. Fasteners are the general term for a class of mechanical parts used when two or more parts (or components) are fastened and connected into a whole. In order to obtain ideal performance and organization in the production of fastener wires, the key is Select the appropriate spheroidizing annealing process.

The Chinese invention patent with the publication number CN1245524C introduces a low-carbon low-alloy steel spheroidizing annealing process. The workpiece is placed in the annealing furnace, and the heating temperature and time are controlled to carry out the annealing process. It is characterized in that the following method is adopted in the annealing process And steps: a. Use a mechanical pump to quickly extract the air in the annealing furnace. When the vacuum degree of 10-50pa is formed in the furnace, the mechanical pump stops working, and then feeds industrial nitrogen with a purity of 99.8% into the furnace. When the pressure in the furnace reaches When the positive pressure is 1500-2500pa, stop nitrogen filling; b. With the slow pressure release in the furnace, when the pressure drops to 150-300pa positive pressure, repeat step a; c. The above "intermittent vacuum + nitrogen filling" The steps are repeated until the annealing process ends. The spheroidizing annealing of fastener wires according to the existing process is too complicated, and the quality is difficult to control. The metallographic structure is uneven, the hardness is high, and the toughness is poor. A large number of fastener wires have cracks after cold forming. Especially for the production of riveted screw fasteners, the requirements are more stringent, which often fail to meet the needs of users, which directly leads to the scrapping of the produced fastener wires, seriously affecting the quality and yield of fastener wires.

Invention content:

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a spheroidizing annealing process for low-hardness fastener wires. The metallographic structure of the fastener wires treated by the process method of the present invention is uniform and fine-grained. Particles, low hardness, high toughness, high ductility, meet the requirements of fastener products that are difficult to form by multiple plastic processing, and the product has a low cracking rate.

The purpose of the present invention is achieved through the following technical solutions:

A spheroidizing annealing process for a low-hardness fastener wire, which comprises the following steps in sequence:

A. Put the fastener wire in the heat treatment furnace, fill the heat treatment furnace with protective gas, then raise the temperature in the furnace to 710-730°C, and keep it warm for 2-4 hours;

B. Cooling in the first stage: Cool the temperature in the furnace to 660-680°C at a rate of 20°C/hour, and keep it warm for 2-4h;

C. Second-stage cooling: continue to cool the temperature in the furnace to 600-620°C at a rate of 10°C/hour;

D. The third stage of cooling: the fastener wire is naturally cooled to room temperature.

Preferably, it comprises the following steps in turn:

A. Put the fastener wire in the heat treatment furnace, fill the heat treatment furnace with protective gas, then raise the temperature in the furnace to 720°C, and keep it warm for 3 hours;

B. Cooling in the first stage: Cool the temperature in the furnace to 670°C at a rate of 20°C/hour, and keep it warm for 3 hours;

C. Second-stage cooling: continue to cool the temperature in the furnace to 610°C at a rate of 10°C/hour;

D. The third stage of cooling: the fastener wire is naturally cooled to room temperature.

Wherein, in the step A, the heat treatment furnace is first filled with industrial nitrogen with a purity of 99.99%, and when the temperature in the furnace rises to 500° C., the industrial nitrogen is turned off, and methanol cracking gas is charged into the heat treatment furnace.

Wherein, after the step C is completed, the methanol cracking gas is closed, and the heat treatment furnace is filled with industrial nitrogen with a purity of 99.99%.

Wherein, in the step A, the temperature in the furnace is raised to 710-730° C. at a rate of 90-120° C./hour.

Wherein, the cooling in the first stage and the cooling in the second stage are performed by air cooling.

Wherein, the material of the fastener wire is ultra-low carbon steel CH1T material for cold heading.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

In the spheroidizing annealing process of a low-hardness fastener wire provided by the present invention, the temperature is first raised to 710-730°C for heat preservation, because if the heat preservation temperature is too high, cementite will be uniformly dissolved in austenite, thereby forming Single and uniform austenite structure, according to the spheroidization theory, uniform austenite transforms into granular cementite structure after cooling, and it is difficult to transform into spherical cementite structure. Similarly, when the holding temperature is low, carburizing The body is not fully dissolved, and the transformed structure is massive pearlite, and the distribution is uneven, and it is difficult to obtain spheroidized pearlite with uniform structure. Then adopt the slow cooling method of the first stage cooling, the second stage cooling and the third stage cooling, so that the cementite spheroidization rate gradually increases, and the uniformity is better. If the cooling speed is too fast, the obtained spheroidized structure is not good. Uniform; if the cooling rate is too slow, the flaky cementite in the original structure is difficult to break, and a good spheroidizing effect cannot be achieved. In summary, the present invention adopts the process of heating up, heat preservation, first-stage cooling, second-stage cooling and third-stage cooling to achieve better spheroidizing annealing effect, and the fastener wire has high ductility and low hardness, which is suitable for subsequent plasticity. Processing and forming, the advantages of low cracking rate of product forming, at the same time, the process is simple, the requirements for equipment are not high, the production efficiency is high, and the cost is low; after testing, the processed fastener wire can reach the following technical indicators: hardness (HV0 .3): 90-100; tensile strength: 280-310 MPa, grain size: 10-12.

Detailed ways:

In order to facilitate the understanding of those skilled in the art, the present invention will be described in further detail below in conjunction with examples, but the protection scope of the present invention is not limited to the following examples.

Example 1

A spheroidizing annealing process for a low-hardness fastener wire, which comprises the following steps in sequence:

A. Put the fastener wire made of CH1T in a heat treatment furnace, fill the heat treatment furnace with industrial nitrogen with a purity of 99.99%, and raise the temperature in the furnace to 500 °C at a rate of 90 °C/hour, then close Process nitrogen, fill the heat treatment furnace with methanol cracking gas, continue to heat up to 710 ° C, and keep it for 4 hours;

B. The first stage of cooling: Cool the temperature in the furnace to 680°C at a rate of 20°C/hour through air cooling, and keep it warm for 2 hours;

C. Second-stage cooling: continue to cool the temperature in the furnace to 600°C at a rate of 10°C/hour by air cooling, close the methanol cracking gas, and fill the heat treatment furnace with industrial nitrogen with a purity of 99.99%;

D. The third stage of cooling: the fastener wire is naturally cooled to room temperature.

The fastener wire treated in this embodiment was tested for hardness, and the Vickers hardness was 90, the tensile strength was 280 MPa, and the grain size was 11. .

The metallographic analysis of the fastener wire treated in this embodiment was carried out laterally under an optical microscope (500×), and it was found that granular (or spherical) carbides were dispersed on the ferrite matrix, and the dispersion was uniform.

In short, the metallographic structure of the fastener wire processed by the process method described in the present invention is uniform, fine grained, low in hardness, high in toughness, and high in ductility, which meets the requirements for fastener products formed by multiple plastic processing with high difficulty. Requirements, product molding cracking rate is low.

Example 2

A spheroidizing annealing process for a low-hardness fastener wire, which comprises the following steps in sequence:

A. Put the fastener wire made of CH1T in the heat treatment furnace, fill the heat treatment furnace with industrial nitrogen gas with a purity of 99.99%, and then raise the temperature in the furnace to 500°C at a rate of 110°C/hour, then turn off Process nitrogen, fill the heat treatment furnace with methanol cracking gas, continue to heat up to 720°C, and keep warm for 3h;

B. The first stage of cooling: Cool the temperature in the furnace to 670°C at a rate of 20°C/hour through air cooling, and keep it warm for 3 hours;

C. Second-stage cooling: continue to cool the temperature in the furnace to 610°C at a rate of 10°C/hour by air cooling, close the methanol cracking gas, and fill the heat treatment furnace with industrial nitrogen with a purity of 99.99%;

D. The third stage of cooling: the fastener wire is naturally cooled to room temperature.

The hardness of the fastener wire treated in this embodiment was tested, and the Vickers hardness was 94, the tensile strength was 291 MPa, and the grain size was 10 grades. .

The metallographic analysis of the fastener wire treated in this embodiment was carried out laterally under an optical microscope (500×), and it was found that granular (or spherical) carbides were dispersed on the ferrite matrix, and the dispersion was uniform.

In short, the metallographic structure of the fastener wire processed by the process method described in the present invention is uniform, fine grained, low in hardness, high in toughness, and high in ductility, which meets the requirements for fastener products formed by multiple plastic processing with high difficulty. Requirements, product molding cracking rate is low.

Example 3

A spheroidizing annealing process for a low-hardness fastener wire, which comprises the following steps in sequence:

A. Put the fastener wire made of CH1T in a heat treatment furnace, fill the heat treatment furnace with industrial nitrogen with a purity of 99.99%, and raise the temperature in the furnace to 500°C at a rate of 120°C/hour, then close the process Nitrogen, fill the heat treatment furnace with methanol cracking gas, continue to heat up to 730°C, and keep warm for 2h;

B. The first stage of cooling: Cool the temperature in the furnace to 660°C at a rate of 20°C/hour through air cooling, and keep it warm for 4 hours;

C. Second-stage cooling: continue to cool the temperature in the furnace to 620°C at a rate of 10°C/hour through air cooling, close the methanol cracking gas, and fill the heat treatment furnace with industrial nitrogen with a purity of 99.99%;

D. The third stage of cooling: the fastener wire is naturally cooled to room temperature.

The fastener wire treated in this embodiment was tested for hardness, and the Vickers hardness was 100, the tensile strength was 310 MPa, and the grain size was 12 grades. .

The metallographic analysis of the fastener wire treated in this embodiment was carried out laterally under an optical microscope (500×), and it was found that granular (or spherical) carbides were dispersed on the ferrite matrix, and the dispersion was uniform.

In a word, the metallographic structure of the fastener wire processed by the process method described in the present invention is uniform, fine-grained, low in hardness, high in toughness, and high in ductility, which meets the requirements for difficult multiple plastic processing. Fastener product requirements, product molding cracking rate is low.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, so equivalent changes made according to the patent scope of the present invention are all included in the protection scope of the present invention.

Claims (7)

1. a carbide annealing process for soft fastening piece wire rod, is characterized in that: it in turn includes the following steps:

A, fastening piece wire rod is placed in to heat treatment furnace, in heat treated stove, is filled with shielding gas, then the temperature in stove is risen to 710-730 ℃, insulation 2-4h;

B, first stage are cooling: the temperature in stove is cooled to 660-680 ℃, insulation 2-4h with the speed of 20 ℃/h;

C, subordinate phase are cooling: continue the temperature in stove to be cooled to 600-620 ℃ with the speed of 10 ℃/h;

D, phase III are cooling: wire rod naturally cools to normal temperature.

2. the carbide annealing process of a kind of soft fastening piece wire rod according to claim 1, is characterized in that: it in turn includes the following steps::

A, fastening piece wire rod is placed in to heat treatment furnace, in heat treated stove, is filled with shielding gas, the temperature in stove is risen to 720 ℃, insulation 3h;

B, first stage are cooling: the temperature in stove is cooled to 670 ℃, insulation 3h with the speed of 20 ℃/h;

C, subordinate phase are cooling: continue the temperature in stove to be cooled to 610 ℃ with the speed of 10 ℃/h;

D, phase III are cooling: fastening piece wire rod naturally cools to normal temperature.

3. the carbide annealing process of a kind of soft fastening piece wire rod according to claim 1 and 2, it is characterized in that: in described steps A, first in heat treated stove, be filled with purity and be 99.99% industrial nitrogen, when the temperature in stove is warming up to 500 ℃, close industrial nitrogen, in heat treated stove, be filled with dissociated methanol gas.

4. the carbide annealing process of a kind of soft fastening piece wire rod according to claim 1 and 2, is characterized in that: after described step C finishes, close dissociated methanol gas, be filled with purity and be 99.99% industrial nitrogen in heat treated stove.

5. the carbide annealing process of a kind of soft fastening piece wire rod according to claim 1, is characterized in that: in described steps A, the temperature in stove is warming up to 710-730 ℃ with the speed of 90-120 ℃/h.

6. the carbide annealing process of a kind of soft fastening piece wire rod according to claim 1, is characterized in that: cooling and described subordinate phase of described first stage is cooling is to be undertaken cooling by air-cooled mode.

7. the carbide annealing process of a kind of soft fastening piece wire rod according to claim 1, is characterized in that: the material of described fastening piece wire rod is ultra low-carbon steel CH1T material for cold-heading.